Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
phosphor bronze (PB), brass (BRS), stainless steel (SS), and gun metal (GM), were measured via a pendant drop method at 25°C. The average surface tension values on these substrates, alongside the general physicochemical properties of the esters, are summarised in Figure 7. The average surface tension values in descending order were LCTE > LCEE > LCCE > LCLE; the greater surface tension values found in LCTE and LCEE imply the greater intermolecular forces and degree of polarity within these esters with three-membered rings.
Figure 8: SP and COF of LCLE, LCCE, LCEE, LCTE Synthesised Esters on Substrates [11]
Figure 7: Physicochemical Properties of LCLE, LCCE, LCEE, LCTE Synthesised Esters [11]
Based on the surface tension values and contact angles of the esters across all substrates, the SP of the esters in ascending order was LCEE < LCTE < LCLE < LCCE. The less polar lubricants, LCCE and LCLE, exhibit high SP values that suggest their weak Van der Waals interactions with polar substrates and inability to protect the substrate from wear. Meanwhile, polar lubricants like LCEE and LCTE offer lower SP values that exemplify their strong interaction with substrates and wettability to protect surfaces. Moreover, SP models are useful in predicting the coefficient of friction (COF) trend between lubricants and substrates with higher SP values implying higher COF values. The direct correlation between SP and COF is verified with a ball-on-disc friction test to precisely measure the COF of each lubricant on different substrates, which in descending order was LCCE > LCLE > LCEE > LCTE. The values of SP and COF of each lubricant with its respective substrate are listed in Figure 8.
The exceptional wetting behavior of LCEE and LCTE highlights the potential future applications of novel “triangle esters” for synthetic lubricants over traditional linear and acyclic esters lubricants, like LCLE and LCCE. Nonetheless, this study limits its results to the substrates chosen and specified lubricants of the same carbon chain length, requiring further studies with other types of lubricants and higher-pressure environments. From a holistic view, this innovative research has expanded the field of synthetic lubricants by introducing a preliminary, improved classification of synthetic esters that may widen future industrial and consumer options. [11]
Conclusion
Looking into the 21st century, synthetic lubricants are gradually becoming the new frontier of tribology as researchers recognise the limited understanding of mineral oil in conventional lubricants. Cross examinations between conventional and synthetic lubricants prove the latter can be more energy- efficient, and possibly provide a long-term solution to global friction and wear prevention. As this field of study continuously expands with the creative synthesis of unconventional organic sources, like waste plastic and triangle esters, it is feasible that these new, green synthetic methods and variety could eventually substitute more conventional lubricants on
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